The invention relates to a storage apparatus and management unit setting method, and is suitable for use in, for example, a storage apparatus that provides a host apparatus with a storage area that can have its capacity dynamically extended.
In storage systems for storing data using a storage apparatus, there is a conventional management method in which plural hard disks are managed in an RAID (Redundant Array of Independent/Inexpensive Disks) system. At least one logical volume is formed in a physical storage area provided by multiple hard disks.
In recent years, a dynamic storage area assignment technique has being proposed in which: a host apparatus is provided with a virtual volume by plural logical volumes without creating a logical volume having fixed capacity in a storage area of a hard disk; and a storage area in each logical volume are dynamically assigned to the virtual volume in response to a request from the host apparatus (e.g., see JP2003-015915 A). Dynamic capacity extension for a virtual volume can be realized with the dynamic storage area assignment technique.
However, in the above dynamic storage area assignment technique, when a page size, which serves as a management unit for managing a storage area in a logical volume on a predetermined-area basis, is too large with respect to the actual access from a host apparatus, the page size is too large for the data stored for the page size. Thus, it is considered that a useless area increases in the storage area in the logical volume, which leads to the reduced usage efficiency of the storage area in the logical volume.
On the other hand, when the page size is too small, management information for managing the page size increases, so a large system area for storing the management information needs to be reserved. This may result in a system area insufficiency. Also when the page size is too small, the number of accesses to the management information increases. This may lead to reduced performance in the entire storage apparatus in terms of access to the host apparatus.